- From: Anton Prowse <prowse@moonhenge.net>
- Date: Sun, 27 Mar 2011 17:45:29 +0200
- To: "www-style@w3.org" <www-style@w3.org>
- CC: Alan Gresley <alan@css-class.com>
On 27/03/2011 17:32, Alan Gresley wrote: > On 28/03/2011 12:31 AM, Anton Prowse wrote: >> 10.6.4 concerning the height of absolutely positioned elements says: >> >> # [...] the static position for 'top' is the distance from the top >> # edge of the containing block to the top margin edge of [...] >> >> But the vertical margin edges are not well-defined for elements whose >> margins participate in margin collapsing. This is most noticeable for >> self-collapsing elements, such as in the following test case in which >> there is no sensible relationship between the border box position of the >> "tricky" element (as determined by 8.3.1) and its 20px bottom margin: >> >> <div style="border-bottom:1px solid"></div> >> <div id="tricky" style="margin-bottom:20px"> >> <div style="margin-top:10px"></div> >> </div> >> <div style="border-top:1px solid"></div> >> >> For the most part this glitch doesn't cause us any problem since the >> spec avoids (albeit probably unconsciously) identifying individual >> margin pieces from amongst a collapsed margin lump. However, 10.6.4 >> relies on identifying the top margin edge of a box which may very well >> participate in margin collapsing. >> >> What should we do to fix this? Where should the absolutely positioned >> element be drawn in the following test case, and why? >> >> <div style="border-bottom:1px solid; margin-bottom:20px"></div> >> <div style="position:absolute; width:100px; height:100px; background: >> yellow; margin-top:10px"></div> >> <div style="border-top:1px solid; margin-top:20px"></div> >> >> There's no interop on this issue, but that's because Fx and IE don't >> perform tentative margin collapsing at all for abspos in order to >> determine their static position. > > > This is since the margins of elements with position absolute do not > collapse [1] 8.3.1. Alan, we're talking about the calculation of the _static position_ of absolutely positioned elements. Cheers, Anton Prowse http://dev.moonhenge.net
Received on Sunday, 27 March 2011 15:46:02 UTC